Teachers are able to give lessons in homophobia, but need to feel supported by their school leaders to do so, according to HuffPost blogger Shaun Dellenty, the founder of the charity and deputy head of Alfred Salter Primary School in London, said.

Mr Dellenty, who is due to talk about the issue at the London Festival of Education later this month, cites evidence which he says shows that 99% of all lesbian, gay and bisexual schoolchildren hear the word "gay" being used in a derogatory way on a regular basis.

"Whole school teaching and learning around the appropriate use of the word gay needs to take place in every school; it is not difficult to teach the varying word use of the word gay and to then clarify and agree that the word gay is not used as a pejorative in schools," he said.

"This is no different from teaching about racial slurs and teachers have the skills they need - they just need to feel supported by school leaders to go ahead with the work.

"We need to celebrate diversity. There is a historically vast gap in teacher training on the matter.

Mr Dellenty, who started teaching in 1996 and came out to his whole school community 14 years later, also said that a teacher who feels unable to reveal their sexuality can invest a "huge amount of emotional energy" in hiding their identity.

This can be exhausting for the teacher, and detrimental to pupils, he said.

"Being authentic enables teachers to fulfil their potential as practitioners and this in turn impacts positively on pupil progress and therefore standards."

He adds: "That some teachers still have to pretend they are single or use the word 'her' instead of 'him' when talking about their partner, because it's 'not the appropriate thing to do', is simply ridiculous.

"There are still some headteachers, especially in faith schools, who tell gay teachers that their 'lifestyle choice' is at odds with the school ethos.

"They fear negative responses and want to 'seek permissions' from parents, governors or people of faith."